A cryopump is conventionally used for evacuation of a vacuum chamber (that may be called as a process chamber) of a semiconductor manufacturing apparatus or the like in order to keep the inside of the vacuum chamber vacuum.
An exemplary use of the cryopump described in Japanese Patent Laid-Open Publication No. 2000-274356 is shown in FIG. 1 (plan view) and FIG. 2 (vertical cross-sectional view).
The cryopump 20 includes a two-stage GM (Gifford-McMahon) expansion type refrigerator 24 that works by receiving supply of compressed helium gas from a compressor 22, for example. The refrigerator 24 includes a first (cooling) stage 26 and a second (cooling) stage 28 having a lower temperature than the first stage 26. A heat shield 30 is connected to the first stage 26, thereby preventing a radiation heat from entering the second stage 28 and a cryopanel 34. A louver 32 is provided in a vacuum-chamber side opening of the heat shield 30. To the second stage 28 is connected the cryopanel 34 (that may be called as a second-stage panel because it is connected to the second stage 28) including activated charcoal 36.
In FIGS. 1 and 2, the reference numeral 40 denotes a rough valve to which a dry pump (not shown) is connected, the reference numeral 42 denotes a relief valve for releasing a gas accumulated in the cryopump, the reference numeral 44 denotes a purge valve for introducing a purge gas (e.g., nitrogen gas), the reference numeral 46 denotes a pressure sensor, the reference numeral 48 denotes a connector for a temperature sensor, and the reference numerals 48a and 48b denote temperature sensors for the first stage 26 and the second stage 28, respectively.
The cryopump 20 having the above structure is connected to a vacuum chamber 10 via a gate valve 12. The louver 32 and the heat shield 30 that are cooled to about 40 K to about 120 K cool a gas having a relatively high freezing point such as water vapor so as to condense that gas. Moreover, the cryopanel 34 cooled to 10 K to 20 K cools a gas having a low freezing point such as nitrogen gas or argon gas so as to condense that gas. A gas that is not condensed by the above cooling, such as hydrogen gas, is absorbed by the activated charcoal 36. In this manner, gases inside the vacuum chamber 10 are discharged.
As described above, the cryopump 20 is an accumulation type pump and therefore requires a regeneration process for discharging accumulated gases to the outside of the cryopump 20 when the amount of the accumulated gases reaches a certain amount.
Examples of conventional regeneration methods include (1) a method in which temperatures of the louver 32, the heat shield 30, and the cryopanel 34 are increased by using a heater or the like at the same time as start regeneration and thereafter a purge gas (e.g., nitrogen gas) is kept flowing, as described in Japanese Patent Laid-Open Publications Nos. Hei 8-61232 and Hei 6-346848, and (2) a method in which roughing and purging are repeated (hereinafter, referred to as rough-and-purge), as described in Japanese Patent Laid-Open Publication No. Hei 9-14133.
FIG. 3 shows an exemplary procedure using the rough-and-purge, and FIG. 4 shows an example of changes in a pressure and a temperature.
In FIG. 3, Step 100 is a procedure for increasing temperatures of respective parts in a cryopump case, Step 110 is a procedure of the rough-and-purge, Step 130 is a procedure of buildup determination for detecting that discharge of water or gas is finished from a pressure increase ratio when the roughing by the vacuum pump is stopped, for example, and Step 140 is a procedure for cooling down the parts to temperatures that are required for an operation of the cryopump.